CrOx/SiO2 catalysts were characterized and their activity in the dehydrogenation of i-butane was measured. Cr loading of the catalysts was between 1.1 and 11 wt% and preparation was by impregnation. The consumption of isolated OH groups of SiO2 upon deposition of CrOx was followed by DRIFT-IR. The presence of unreacted OH groups in the calcined catalyst at high loadings of Cr and the formation of alpha-Cr2O3 (XRD) showed, however, the tendency of CrOx to form clusters rather than a well-dispersed phase on SiO2. After calcination, 0.8-1.0 wt% Cr was stabilized in 6 + oxidation state (UV-VIS). On the basis of H-2-TPR measurements it was suggested that these Cr6+ were stabilized by anchoring on SiO2 or on the alpha-Cr2O3/SiO2 formed with increasing Cr loading. The activities of the CrOx/SiO2 catalysts were studied in the dehydrogenation of i-butane at 540 degrees C by monitoring the product distributions with a rapid FT-IR gas analyzer. The dehydrogenation activity is attributed to redox Cr in 3+ and 2+ oxidation states and tentatively to part of the nonredox Cr3+ Th, relatively low selectivity of CrOx/SiO2 at low loadings of Cr was evidently due to the presence of Cr2+ directly anchored to SiO2.